IIT Guwahati develops self-healable amphiphobic solid slippery coating

GUWAHATI: Indian Institute of Technology (IIT) Guwahati researchers have developed a self-healable amphiphobic solid slippery coating that exhibits sliding of droplets of various liquids - including of water, polar and non-polar organic solvents, edible oil, motor, engine oil, and crude oils. It also shows self-healing of repetitive (50 times) physical damages in less than 1 minute and the embedded slippery property remained intact.

The research team of IIT Guwahati, which included research scholars Manideepa Dhar, Avijit Das, Dibyangana Parbat and led by Dr Uttam Manna, Associate Professor, Department of Chemistry & Centre for Nanotechnology, has developed a simple and scalable fabrication of a non-fluorinated, substrate-independent, and self-healable amphiphobic solid slippery coating. This coating exhibits sliding of droplets of various liquids-including water, polar organic liquids (ethanol, 1-propanol, 1-hexanol, DMSO, DMF), and non-polar (decane, dodecane, diiodomethane) solvents, edible (vegetable oil), motor, engine (petrol, diesel, kerosene) and crude oils. This coating shows self-healing of repetitive (50 times) physical damages in less than 1 min and the embedded slippery property remains intact. Also, this surface can withstand prolonged exposures to various complex aqueous phases (pH 2, pH 12, SDS, and DTAB contaminated water, river water, seawater) and UV irradiation for 15 days. Substrate independence and scalable fabrication process are other crucial features of this current design.

This coating has been successfully developed on various substrates such as glass, aluminum foil, printed paper, plastic, etc., as well as geometrically complex objects like curved surfaces, inside of a glass bottle, etc. The simple fabrication process also allows coating on a large glass object (1325 cm2).

Bio-inspired surfaces where water / oil droplets effortlessly roll or slide off have enormous promise in developing materials related to energy, biomedical applications, etc. However, due to the delicate nature of the trapped metastable third phase (i.e., trapped air layer in textured surface) responsible for heterogeneous liquid wetability, these surfaces frequently failed to withstand abrasive conditions such as elevated temperature and pressure, alkaline and acidic environments, etc. To address this critical problem of stability, ultra-smooth and homogeneous slippery surfaces were developed following different unique approaches.

When an insect sits on the walls of nepenthes pitcher plants, it slides into a chamber filled with digestive juices. Researchers have attempted to build surfaces that are slippery to external fluids based on the slippery characteristics of the nepenthes pitcher plant. Aizenberg and her co-workers mimicked the technique of slipperiness used by the nepenthes pitcher plant and have developed an omniphobic slippery liquid-infused porous surface (SLIPS) through the strategic infusion of fluorinated liquid lubricant in an appropriately decorated porous and featured interface. This defect-free, ultra-smooth, lubricant-infused slippery surface has a much-needed self-repairing ability, allowing it to endure severe physical abrasions. However, the leaching of infused fluorinated lubricant from the surface limits the ability of the surface to be used for more extended periods and contaminates the beaded liquids.

To avoid this problem of infused fluorinated lubricant leaching, IIT Guwahati's team has developed this simple and scalable fabrication of a non-fluorinated, substrate-independent, and self-healable amphiphobic solid slippery coating. A hydrophilic porous polymeric coating has been strategically infused with a selected comb-like polymer to develop a crystalline network. Eventually, a self-healing and amphiphobic solid-slippery interface was obtained at the end.

The bottle that is decorated with such coating allowed traceless dispense of a viscous food item, for example honey, with ease. Moreover, such coating protected the display of cell phones from any aqueous and oily contaminations. The prepared optically transparent solid slippery coating displayed self-cleaning ability.

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